At the present time long-wall coal mining operations are generally limited to a "single-pass" technique in order to comply with government regulations for dust control. The single-pass technique allows mining only in the direction of the flow of ventilation air through the underground area. In this way, the mine workers who operate the shields and perform other mining related functions trail the generated dust and occupy an area of fresh air as the ventilation flow carries the dust forward, away from the miners. However, shearer operators may be exposed to dust generated by the trailing cutter drum. A long-wall shearer generally has two cutter drums, an upper, leading drum and a lower, trailing cutter drum. Since the trailing cutter drum is lower than the leading cutter, it generates less dust. This dust can be controlled by conventional techniques such as bit sprays located along the cutter drum periphery, special cutter drum bit shapes, reduced cutter drum revolution speeds and air moving sprays also known as "shearer clearers".
A major problem is encountered when attempts are made to mine in a direction opposite to or against the flow of ventilation air. In such an operation, the shearer operator is exposed to the dangerously high levels of dust generated by the upper cutter drum and carried back to the shearer operator by the ventilation air flow. Other miners are exposed to the dust generated by both cutter drums. To date, no satisfactory dust control technology has been developed which would allow long-wall coal mining in a direction against the ventilation flow without severely reducing cutting speeds in order to comply with governmental dust control regulations.
The problem remains despite a great economic incentive to develop the two-pass technique in order to increase a mine's productivity potential. Various types of dust collectors have been experimented with but have proven unsuccessful for a number of reasons. Foremost among the reasons is either the dust collectors could not remove sufficient quantities of dust from the air or the collectors or filters have been so large that their use is precluded by their vulnerability to damage or their interference with the mining operation itself.
The present invention allows increased coal production which in turn helps solve the national energy problem.